Prior art type display drivers such as those used with the Hewlett Packard HDSP-88XX Series of 101-element LED linear arrays (bar graphs) rely on standard TTL parts. To further explain, the HDSP-88XX is a 101 element bar graph array. The linear array is arranged as ten groups of ten LED elements plus one additional element. The ten elements of each group have common cathodes. Like elements in the ten groups have common anodes. The device is addressed via 22 single-in-line pins extending from the back side of the display. A major problem with this type of device is that in some cases, undesirable "ghosts" or "phantom bars" can occur on the display. These ghosts or phantom bars are due in part to the inefficient logic/timing schemes employed in the prior art. These errors, which are obviously undesirable, are due largely to the fact that in this, and other prior art display driver schemes, as one LED is being turned off another is being turned on at the same time.
To summarize, a drawback with the prior art is that there is no assurance that only one segment will be on at a time. This leads to the problems of "ghosts" or "phantom" bars.
Another problem with the prior art display drivers is that, typically, they are microprocessor driven. While microprocessor programmability may be desirable in some situations, their faster clocks (e.g., in the MHz range) introduce or increase the likelihood of radio frequency interference (RFI) which ca necessitate heavy shielding. This is also obviously undesirable.